Telephone apparatus



2 SHEETS- SHEET 1 zooo sooo'wo Sept. 2, 1952 s. D. vlGREN ET AL TELEPHONE APPARATUS Filed May 17, 1950 S. D. VIGREN ET AL Sept. 2, 1952 TELEPHONE APPARATUS 2 SHEETS--SHEET 2 'Filed May 17. 1950 Patented Sept. 2, 1952 UNITED STATES PATENT orffrlcr;

TELEPHGNE APPARATUS `Sten Daniel Viglcn andl Gustar` Ernfrid. Gustafsson, Stockholm, Sweden Application May'17, '1950, Serial No. 162,451

In Sweden January '-1f6, 1948.

9 Claims.

betweenA paper Vwashers or the like to .the .comVv tainer. ASuch a diaphragm has a frequency curve, which-is lowin `the 4bass land the intermediate-register, but which otherwiseis relatively goody and'Y free from resonance peaks.

This invention 'offers :a new type .of .transmite ter, which is provided with a diaphragm kdissimilarly :movable in one and 'in theother direction,y and which oliers a substantially better result A.than that offered :by known transmitters, due vtothe fact that the new type of :transmitter has a substantially rstraight frequency curve at output levels very much higher than those of known transmitters.'-

The inventors have found vthat in .orderzto dbftain the fbestr possible result Ltheconstruction and arrangementnof the yelectrodes should be. taken intoconslderatlon. Y

When a diaphragm is` actuated by a sound wavazit will ,alternately be` exposed to pressure and: pull in step-With the,frequency of the sound waves. The. .diaphragm vibrates with the sound Wad/'8,v und;k its energy-0f motionshall be con verted into variation o f the resistance of. the

granulark carbon by increase and c lefnease of `its compression.

AAs the granular .carbon has a certain mass the-,most effective` variation of die resistance will take place, between the diaphragm and the adjacent layer of granular carbon.

The energy of motion shall accordingly be transmittedgto an effective surface layer ad jacent' the diaphragm yand not to the surfaces of comminuted carbon particles within .the mass of themgranular carbon or to a surfacer layer adjacent an insulating surface.

It ls this surface layer, which in known transmitters is exposed to overloads at great ampl tudes of. the diaphragm, and which overload by and by causes a heavily increasing distorsion and rreduced sensitivity. This result is obviously related, to afchange of the resistance variation` curve of the granular carbon.

The inventars have found. that an increased depthpf .granular :carbon 'does not lessen the 4risk of overloadl According to a .feature sift-his invcnticnfthe surface area of the vgranular carbon adjacent' the .diaphragm is of a size relatively large compared to that vof known transmitters. The depthof the granular carbon mass should ohlyfbsilm* cient to give the necessary initialpressurcnbstween the granular carbon particles. Thefprcs.-

sure, between the granular carbon and the da@ phragm in non-actuated position shouldnill? tbe allowed `to* be lsssthan zero! .when the diaphragm ispulledfoutwards at .1a maximum amplitudes.

chosen, that the opera-tins, value lof the resistance would cbe -locatedin the-.middle of isaidfranscr when the diaphragm is in normal non:operatedr The, surface. of the. diaphragm adiasenrrue,

granular carbon Y.should preferably .ccnsis d .of

air:

bon, for examplsacarbcn disc, ofsuena-diameteronlyl that Lthe.granular carbon champcrsare well closed; because the carbon surface Agives a.

diaphragm. The variation ofresistance. is, hcwever substantially linear within the range to be used.

rcction from thcgra-nular carbon, upon: lowering 0f thefairrpressure, should according t0 a feature oithis invention: be `heavily dampened -to fp-re-4 vent too.- much. lowering yof the pressure YV0f:y the granular carbon. If the said. .pressure-Were lowered .too much, distortion wouldresult! duetoN the` fact .that for ra vcertain air pressurethe pres-l sure phase would cause less variationof resistance in the vgranular :carbon mass than .that .of the pulling phase. n

The brest result is obtained, .the entire prese sure phase is transmitted 4,to .the .granular care bon mass, in which case the diaphragm at-the periphery should becompletcly free to more, to-

wards the .granular carbon` mass.` No pressure' or Ipower robbing details should vbe allowed'iat thc-range tc be used f or variaticn ci :resistance between this granular carbon particlessnd the.; diaphragm is v'limitedlv the-initial pressure should; according to da, feature of the. -inventn- :bQxSSJ' This feature increases.: the, A -carhcnsuriace It: increasesrhearily with the amplitude of the movement` of, the

the periphery on the side facing the granular carbon mass, for example paper washers or the like.

At the other side of the diaphragm, however, the diaphragm at the periphery should rest against the transmitter case or its protective lid, so that a heavy dampening action is obtained, when the diaphragm moves in the direction from the granular carbon mass.

This dampening action can be increased by making the diaphragm partly conical, and if desired to stiien it by radial corrugations.

The diaphragm will thus according to this invention be clamped between a fixed peripheral surface at the side of the diaphragm turned from the granular carbon mass and a limited central part of the diaphragm in contact with the said granular carbon mass and with an elastic insulating material surrounding part of said granular carbon mass.

The present telephone transmitter offers several favourable features over those of known transmitters, such as a substantially increased sensitivity, an improved and substantially straight frequency curve, and low distortion.

Its transmission efficiency is l to 2 nepers or about 8 to 17 db higher than that of known transmitters.

Due to these favourable features a perceptibility or degree of articulation of 11/2 nepers or about 13 db is obtained over that of known transmitters.

- 'I'hanks to all these favourable factors a cheap outside telephone plant can be used, in which the line conductors in cables and aerial lines can be made of small diameters. An economical profit can thus be made, when planning a new plant or an extension of an old one.

In an old telephone plant good transmission can be obtained over greater distances than heretofore.

The invention will be better understood by the following description of different non-limiting embodiments of the invention in connection with the accompanying drawings, in which:

Fig. 1 is a vertical section of an embodiment of a transmitter according to the invention.

Fig.'2 and Fig. 3 are sectional and top views respectively of another embodiment of detailsl of the invention.

Fig. 4 and Fig. 5 are sectional views of other embodiments of diaphragme and granular carbon chambers according to the invention.

Fig. 6 shows frequency curves of a transmitter according to the invention and those of two known transmitters.

Fig. '7 is a vertical sectional view of still another embodiment of the invention, and

Fig. 8 is a top view partly in section of the transmitter shown in Fig. 7.

In Fig. l a casing l serves to inclose the working parts of the transmitter and to support a face plate 4 provided with openings l2 to admit sound waves to diaphragm 2, whichin this embodiment is conical and in the center provided with a dome-shaped part l5. The diaphragm is preferably made of an aluminium or magnesium alloy, for example Duralumin. It can be provided with radial corrugations I5. A channel l1 is provided at the periphery of the diaphragm for stiiiening it. The diaphragm at the periphery is pressing against the faceplate 4 or against an intermediate moisture proof noncompressible membrance (not shown).

YIn this embodiment a plane carbon diaphragm 3, the surface of which only slightly exceeds the opening surfaces of the carbon chambers 6 and 8, is glued to or in any other manner is attached to the center of the metal diaphragm 2.

There are two chambers 6 and 8, each lled with a layer of granular carbon. These layers are at one side limited lby carbon electrodes l and 9 and at the other side by the carbon diaphragm 3, whereby the initial pressure between the carbon diaphragm and the granular carbon is so chosen, that the working point of the transmitter in non-operated condition is located at about the middle of the resistance variation curve of the transmitter.

The surface area of the layers of the granular carbon masses should be large compared to the depth of said layers in order to obtain a suitable pressure between the granular carbon masses and the carbon diaphragm.

The granular carbon chambers are laterally inclosed by an elastic insulating material 5, for example an elastic felt, sponge rubber or an elastic sponge-like material of a synthetic resin, for example polyethylene, polytetraiiuorethylene or the like.

Between the granular carbon chambers there is a wall of separation HJ of the same material as the outside insulation 5, which wall of separation can entirely separate the granular carbonv in the chamber 6 from the granular carbon in the chamber 8 by giving thel said wall the same height as the outside insulation 5. In Fig.Y l, however, the wall of separation IU is somewhat lower, so that an opening I l is provided between the chambers and the carbon diaphragm, which opening is lled with granular carbon.

By this conducting connection between the chambers interruption of the electrical circuit through the transmitter is prevented, in case the transmitter should Ibe held in such a horizontal position, that the pressure of the carbon diaphragm should be a minimum, for example Zero.

Normally, electric current passes from the granular carbon of one chamber through the carbon diaphragm to the granular carbon of theother chamber. V

In Fig. 2 and Fig. 3 a modification is shown, in which the diaphragm 29 has been provided with two protuberances 23 and 24 dipping into the chambers 'I and 9 respectively. The protuberances are intended to secure electrical connection f between the granular carbon of the respective chambers and the carbon diaphragm 20,'if the granular carbon should be partly lacking and not completely fill the chambers, when in horizontal" position. In this embodiment the insulating wallof separation I0 is cf the same height as the out-`V side wall 5 of the resilient and elastic insulating" material, both kind of walls having been stamped out from a sheet of the desired insulating material of suitable thickness, so that the granular carbon of one chamber is entirely separate from the granular carbon of the other chamber.

In Fig. 3 is shown a top view showing the form of the'granular carbon chamibers 26 and28, the

Vopening surfaces of which, adjacent the carbon diaphragm, are large compared to the surface of the carbon diaphragm. The contact surfaces or" the granular carbon layers are large compared to the depth of the said layers as noticed from Fig. 2 and Fig. 3.v

Fig. 4 shows an embodiment, in whichkv the diaphragm `42 is made in one piece, for example of metal,y and provided with a spherical dome 43'towards the granular carbonchambers 46 andla" The .surfaces :of .thleizcarbon: electrodes-y ;411; :and v 49. are sphericalandiparallel'withrthefsurfaces:of the said dome. The'.:diaphragniiis.,pravlded with a horizontal `ringesliaped.surfacerbetweer the dome and the periphery, which serves as seat for resting the diaphragm*onftheelastic-resilient insulation 45, 50. On account ofthe spherical shape of the dome and of the carbonelectrodeathe granular carbon will bein contact with the diaphragm in'all positions'ofth'e transmitter so that interruption of the circuit is prevented. Y

In Fig. 5"there is shown Aanother embodiment ofzacomposite diaphragmvsimilarto that o`f Figi, but instead fof a vflat carbon` diaphragm 3'Tthereis in` :this embodiment -asmallrcurved carbon or metal-:diaphragm orldisc/SB-a'ttached to the conical. metaly f diaphragm `52 .and its Poutward dome 55. Otherwise the transmitter is constructed as shown in Fig. 4.

In Fig. 6 there are shown actu-al frequency curves for transmitters of different constructions. In the figure cycles per second (c/s) are shown along the :c-axis according to a logarithmic scale, while along the '1J-axis there are shown the output voltages in nepers and decibels (db) at an air pressure of 10 t bar for all frequencies.

The curve 6| is the frequency curve for a transmitter according to the present invention, while the curves 62 and 63 show frequency curves for two different transmitters known in the market.

Curve 6| shows according to measurements of a sample transmitter its superior qualities over the known transmitters, to wit, a particularly straight frequency curve, a high overall transmitting efficiency and low distortion.

In Fig. 7 and Fig. 8 the casing 1I is pressed in one piece from an insulating material, for example a synthetic resin, such as a condensation product of a phenol formaldehyde resin, ureaformaldehyde, polyethylene, polystyrol, polytetrailuorethylene, or the like.

The casing is provided with cutouts for the carbon electrodes 11 and 19, for the granular carbon chambers 16 and 18 and for the elastic and resilient insulating material 15, for example felt, sponge rubber, sponge polyethylene, or the like.

The carbon diaphragm 13 and the conical metal diaphragm 12 attached thereto rest upon the said elastic and resilient insulating material and press against the granular carbon in the same manner as in Fig. 1. The carbon electrodes 11 and 19 are fastened to the casing by means of bolts and nuts 85 and 86 respectively. An insulation 84 covers the bolt heads, so that the granular carbon masses 16 and 18 do not directly contact the bolts.

A face plate 14 provided with holes 82 is attached to the casing and a moisture-proof substantially non-compressible membrane 83 is located between the faceplate and the diaphragm 12. At the periphery the diaphragm is provided with a reinforcement and rests directly on the said membrane 12 and the face plate 14 at a peripheral surface at the other side of the granular carbon chambers, while the opposite peripheral surface is freely movable in the direction of the said granular carbon chambers.

The granular carbon chambers 16 and 18 are separated by a partition 8B. The chambers have the form shown in Fig. 8 similar to that of the chambers 26 and 28 shown in Fig. 3.

As noticed from Figs. 7 and 8 the granular carbon chambers have large surfaces and low loading-capacity areiobtained. v y vThe xcasing 'is :providedawith..two fstuds 81 to center 'the `elastic' insulation layerf 15,l so" that its position .with respectto'.itszpartition.Whichzseparates thegranularcarbonrmasses in'.thefchamberav will .be located 'exactly 'over thexed partition 80. .Thetra-nsmitter y'operates in :amanner similar to that shown in Fig. 1 and Fig. 3;

:Wei-claim: 1.1;A ,itelephonez stransmitter comprising, in

combination, `a granular Vcarbon' 'containing' chamben. a' :stiff diaphragmith'e l central f part of. onei-side of 'said diaphragm .being electrically( conductive :and4 Lre'ciproeating-ly.L` movable in. `op'- erative relati'on"to"fthe "granular carbon ymass :in said chamber, la .fixed .support fonsupporting` only the other side of the diaphragm at its periphery for heavily damping the movement of the diaphragm, when moving away from the granular carbon mass upon being exposed to the rarefaction phase of a sound wave, said other side of the diaphragm at the periphery being entirely free to move towards the granular carbon containing chamber, when the diaphragm is exposed to the compression phase of a sound wave.

2. The telephone transmitter, as set forth in claim 1, in which the said diaphragm between its peripheral and central parts is conical in shape, and in which the central part of the said diaphragm is pressing against the granular carbon in said chamber.

3. The telephone transmitter, as set forth in claim 1, in which the central part of the diaphragm consists of a carbon disk xedly at tached to the diaphragm and normally subjected to resilient pressure against the mass of granular carbon in said chamber.

4. A telephone transmitter comprising, in combination, two granular carbon containing chambers, a stiff diaphragm, the central part of one side of said diaphragm being electrically conductive and reciprocatingly movable in operative relation to the granular carbon in said chambers, whereby the granular masses in the two chambers are connected in series over the electrically conducting central part of said diaphragm, a fixed support for supporting only the other side of the diaphragm at its periphery for heavily damping the movement of the diaphragm, when moving away from the granular carbon upon being exposed to the rarefaction phase of a sound wave, said other side of the diaphragm at the periphery being entirely free to move towards the granular carbon containing chamber, when the diaphragm is exposed to the compression phase of a sound wave.

5. The telephone transmitter, as set forth in claim 4, in which the granular carbon in each chamber is arranged in the form of a thin layer of large surface area in contact with the central part of said diaphragm.

6. The telephone transmitter, as set forth in claim 4, in which the normal pressure between the diaphragm in non-actuated position and the granular carbon mass is substantially about the middle of the range of the pressure Variation of the transmitter, when exposed to sound waves.

7. The telephone transmitter, as set forth in claim 4, which includes a layer of a porous, elastic and substantially resilient substance, on which layer part of the central part of the diaphragm rests while another conducting part of the said central part of the diaphragm rests on the granular carbon masses of said chambers.

8. The telephone transmitter, as set forth in claim 4, which includesra layer of a porous, elastic and substantially resilient synthetic resin in sponge form, on whichY layer part of the central part of the diaphragm rests, While another conducting part of said central part of the diaphragm rests on the granular carbon masses of said chambers.

9. A telephone transmitter. as set forth in claim 1, in which the transmitter comprises a casing of a moulded electrical insulating mate- A rial-containing cavities for the granular.v carbon and for the diaphragm, and a layer of a porous, elastic and substantially resilient substance, on which layer part of the central part of the dia phragm rests, While another conducting part of Number said centi .part` of the diaphragm ifest'sn the' The following references are of record in the le of this patent:

UNITED STATES PATENTS Name Date 575,887 Hardegen Jan. 26, 1897 1,388,963 Marr Aug. 30, 1921 1,406,833 Finley Feb. 14, 1922 1,815,987 Peterson July 28, 1931 2,042,822 Bennett June 2, 1936 Hassan June 27, 1950 

